Microwave Magnetic Properties and Natural Resonance of e-Co Nanoparticles

Owing to the novel crystal structure, ε-Co nanoparticles with an average diameter of 12 nm are synthesized and the microwave magnetic properties of the epoxy resin composite with 50voi% ε-Co particles are measured in the frequency range 0.1-7 GHz. The experimental resonance frequency （4.7 GHz） matches well with the values obtained by the theoretical calculation with the Kittel equation and fitting the experimental permeability dispersion curve via the Landan-Lifshitz equation. Hence the resonance peak is attributed to natural resonance mode. This work is believed to be beneficial for further understanding microwave applications of the novel ε-Co nanoparticles.     

铜催化烯烃氰烷基化成环合成含氰吲哚酮

发展一种简单、高效的铜催化活泼烯烃氰烷基化成环合成吲哚酮的方法。 在CuI/DTBP(叔丁基过氧化物)催化作用下, N-芳基丙烯酰胺类化合物与α-氰基偶氮试剂发生自由基环化反应, 高效地合成了一系列含α-氰基季碳中心的吲哚酮, 并探讨了其反应机理。 该方法底物适用范围较广、反应体系温和, 催化体系廉价。     

酉羣上的富理埃分析 Ⅳ.关于Peter-Weyl定理

<正> §4.1.Peter-Weyl定理 若G是紧致李羣,f是G上的連續函数.对于任意巳給的ε>0,一定存在在G的农示环(representative ring)上定义的一个函数g,使得|f(σ)-g(σ)|<ε对于任意的σ∈G都成立.这是众所周知的H.Peter与H.Weyl的定理(参閱[7]第Ⅵ章).     

酉羣上的富里埃分析(Ⅲ)富里埃級数的收斂判别法

<正> §3.1.引言 在“酉羣上的富里埃分析Ⅰ,Ⅱ”二文中,我們已經对酉羣上的富里埃級数的Abel求和及Cesaro求和,作了比較仔細的研究,并且給出了富里埃級数的Dirichlet核.本文的主要目的是依靠巳知的Dirichlet核,給出一个比較簡单的收斂判別法.記在n阶酉羣U_n上定义的具有k阶連續微商的函数u(U)的全体为C~k,那末,这个判別法可以叙述     

Calculation of High Frequency Complex Permeability of Carbonyl Iron Flakes in a Nomagnetic Matrix

The carbonyl iron flakes are fabricated by high-energy ball milling. The effective permeability is measured and calculated for the composite consisting of flakes embedded in a nonmagnetic matrix. The magnetic flakes with a shape anisotropy and random spatial distribution of normal direction are considered to calculate the complex permeability of magnetic flake materials. Its analytical model is derived from the Landau-Lifshitz-Gilbert equation and Bruggeman ＇s effective medium theory. The calculated results agree well with the experiment.     

加强型Bi-2212超导股线有限元拉伸性能分析

为探究加强型Bi-2212超导股线的力学性能以及不锈钢包带对超导股线力学性能的影响，运用Ansys软件建立加强型Bi-2212超导股线的三维模型，采用有限元分析方法，对其机械结构进行仿真，模拟高温高压热处理后轴向受拉形变量和应力应变分布情况。仿真结果显示，在同样施加100 N拉力的情况下，与超导原线（Bi-2212超导线）相比，密绕Ni₈₀Cr₂₀包带后的加强型Bi-2212超导股线轴向受拉形变程度减小，约10%;应力应变均降低，约30%。采用Ni₈₀Cr₂₀作为外包带制成的加强型Bi-2212超导股线力学性能显著，是未来超导线发展方向之一。     

回火温度对晶界添加烧结钕铁硼磁体结构演变及磁性提升机理的影响EI北大核心CSCD

采用晶界添加的方法制备了添加Tb65Cu35的烧结Nd-Fe-B磁体,研究了回火温度对晶界添加磁体微结构演变规律及磁性能的影响,并对其性能提升机制进行了分析。结果表明：经910℃一级回火2 h,460℃二级回火2 h的磁体性能最佳,获得了Br=14.14 k Gs,Hcj=12.31 k Oe,(BH)max=47.89 MGOe的磁性能,回火后的磁体的矫顽力从10.21 k Oe提升到12.31 k Oe,增加了约20%,剩磁基本保持不变。矫顽力的提升主要归因于硬磁的(Nd,Tb)-Fe-B壳层以及连续晶界层的形成。通过一阶反转曲线(FORC)对不同回火条件下样品的磁化反转过程进行了分析,可以发现最差回火态晶界添加磁体中有两个峰,然而,最佳回火态的晶界添加磁体只有一个明显的峰,表现出明显的相互作用的单畴晶粒特性,表明最佳回火态磁体内核壳之间具有强的耦合相互作用。     

基于光电氧化还原反应的离子源内分析研究

激光解析离子化过程非常复杂,在这一过程中形成了大量活性物质例如电子、质子、自由基、离子,这些活性物相互作用得到了最终结果.研究这些源内活性物质的反应对于了解MALDI机理、拓展其分析应用有着重要的意义.     

固体吸附剂对CO_2的高压吸附性能研究

在高压吸附仪上研究了硅胶、MCM-41、13X、SBA-15四种固体吸附剂对CO_2的高压吸附性能,考察了温度、压力、结构性质和吸附热对吸附剂吸附量的影响.结果表明,高压下四种吸附剂对CO_2的吸附均属于物理吸附,且随着压力增大吸附剂的吸附性能增强。吸附量的大小变化分为两个阶段,不同阶段影响吸附量的因素不同。四种固体吸附剂的高压吸附实验表明,理想吸附剂的选择需要从吸附量、对温度的敏感性以及孔径大小和分布等综合考虑.     

Microwave absorption properties regulation and bandwidth formula of oriented Y2Fe17N3-δ@SiO2/PU composite synthesized by reduction-diffusion method

As concepts closely related to microwave absorption properties, impedance matching and phase matching were rarely combined with material parameters to regulate properties and explore related mechanisms. In this work, reduction-diffusion method was innovatively applied to synthesize rare earth alloy Y$_{2}$Fe$_{17}$. In order to regulate the electromagnetic parameters of absorbers, the Y$_{2}$Fe$_{17}$N$_{3-\delta }$ particles were coated with silica (Y$_{2}$Fe$_{17}$N$_{3-\delta }$@SiO$_{2}$) and absorbers with different volume fractions were prepared. The relationship between impedance matching, matching thickness, and the strongest reflection loss peak (${\rm RL}_{\rm min}$) was presented obviously. Compared to the microwave absorption properties of Y$_{2}$Fe$_{17}$N$_{3-\delta }$/PU absorber, Y$_{2}$Fe$_{17}$N$_{3-\delta }$@SiO$_{2}$/PU absorbers are more conducive to the realization of microwave absorption material standards which are thin thickness, light weight, strong absorbing intensity, and broad bandwidth. Based on microwave frequency bands, the microwave absorption properties of the absorbers were analyzed and the related parameters were listed. As an important parameter related to perfect matching, reflection factor ($\sqrt {ărepsilon_{\rm r}/\mu_{\rm r}}$) was discussed combined with microwave amplitude attenuation. According to the origin and mathematical model of bandwidth, the formula of EAB (${\rm RL}<-10$ dB) was derived and simplified. The calculated bandwidths agreed well with experimental results.